Drug and temperature influence on the gel state stability of the phospholipid membranes

The amphiphilic phospholipids have two hydrophobic fatty acids separated by charged hydrophilic head groups. They can form bilayers with the interior fatty acids oriented parallel to each other and with the phospholipid heads facing out in contact with water. In order to avoid the complexity of the natural membranes, these bilayers are used as model membranes. At room temperature the model membranes are characterized by a high degree of order in the gel state and, at higher temperature they pass, by a sudden process, in a less ordered state of liquid crystalline type. This phenomenon depends on the phospholipid type as well as on the nature of the possible impurities and it is conditioned by temperature. Our studies were made for dipalmitoylphophatidylcholine model membranes in which some drugs as gramicidin S and nifedipine were added to establish the drug influence on the main phase transition temperature. Gramicidin S decreases the main phase transition temperature, while nifedipine increases the temperature of the main phase transition of DPPC model membranes. Research of the model membranes near the main phase transition can facilitate the understanding of the destabilization by the drug action mechanism of the biological membranes